Optimum standardized ileal digestible tryptophan to lysine ratio for pigs weighing 7–14 kg

• Tryptophan requirement of piglets was studied in a dose-response study.
• Curvilinear-plateau models estimated the optimum SID Trp:Lys to 0.20.
• Fitting broken-line models estimated the optimum SID Trp:Lys to 0.18.
• Minimum 0.20 SID Trp:Lys was concluded as requirement for pigs weighing 7–14 kg.

The objective of the present study was to evaluate the optimum ratio of standardized ileal digestible (SID) Trp to Lys for pigs after weaning. A total of 96 female pigs were allocated to 1 of 6 diets containing 0.13, 0.15, 0.17, 0.19, 0.21, and 0.23 SID Trp:Lys, with 16 individually housed pigs/treatment. The diets contained similar crude protein (154 g/kg), NE (10.5 MJ/kg), and SID Lys (10.9 g/kg). Average daily feed intake (ADFI), average daily gain (ADG), and gain to feed ratio (G:F) were determined for a 21-d period. Blood and urine samples were collected on d 8 and 15. Urea concentration in plasma and urine decreased (P<0.001) concurrently with increasing SID Trp:Lys. The ADFI, ADG, and G:F improved (P<0.001) with increasing SID Trp:Lys. By fitting by a curvilinear-plateau model, minimum SID Trp:Lys to support optimum ADFI, ADG, and G:F were estimated to be 0.20, 0.20, and 0.16, respectively. By fitting a broken-line model, the minimum SID Trp:Lys was estimated to be 0.18, 0.18, and 0.15 for optimum ADFI, ADG, and G:F, respectively. In conclusion, growth performance of pigs weighing 7–14 kg increased up to 0.20 SID Trp:Lys.